Hydraulic accumulators generally have elastomeric sealing elements. Depending on the type of construction of the pressure fluid accumulator as a piston-type accumulator (see in this respect German patent application No. 41 41 929) or as a diaphragm-type accumulator (see in this respect German patent application No. 41 31 524), in dependence on the partial pressure, the gas which is frequently under high pressure in the pressure fluid accumulator diffuses via the seal or diaphragm into the brake fluid. Therefore, the gas volume in these pressure fluid accumulators must be adapted to the diffusion which has to be expected. The use of a pressure fluid accumulator of this type in automotive vehicle brake systems necessitates in particular that the gas is allowed to escape from the brake fluid again in order to prevent malfunction of the brake.
German patent application No. 20 23 637 discloses a pressure fluid accumulator with an intake and outlet connection for a fuel-oil supply system which opens into the housing of the pressure fluid accumulator. A pump is connected to the intake which delivers into a chamber of the pressure fluid accumulator. The pump delivery is interrupted as soon as a tripping pin, connected to a pump switching device, is actuated by way of a pleated bellows which delimits the chamber.
Generic German patent application No. 19 22 070 discloses a pressure fluid accumulator with a pleated bellows which includes a valve element that keeps a fluid port, opening into the housing of the accumulator, closed when the hydraulic accumulator is not acted upon. On the end face of the valve element remote from the fluid port, there is fitted a cylinder which extends into the pleated bellows and, telescopically on a cylinder formed fast with the housing, guides the pleated bellows and the valve element concentrically to the fluid port in the housing. Thus, the exact alignment of the valve element in the housing which cooperates with the pleated bellows is effected by the telescopical arrangement of the two cylinders within the pleated bellows.
An object of the present invention is to develop a pressure fluid accumulator of the above-mentioned type by simple, low-cost and functionally reliable means and to eliminate the shortcomings referred to hereinabove with respect to the state of the art.